Backside Illuminated CMOS Image Sensor Light Shielding

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Solution Overview

Problem

Conventional backside illuminated CMOS image sensors face issues with light shielding, leading to decreased light reception and increased cross-talk due to height differences and refractive path length variations between pixel and surrounding regions, affecting sensitivity and stability of the color filter and lens parts.

Innovation Solution

Forming first sub shielding metal layers at the same height and thickness on both pixel and surrounding regions, with a second shielding metal layer spaced apart and slanted to minimize refractive path length and prevent dishing, while using the same material as the pad for economic manufacturing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the insulating layer is made thick to prevent dishing and ensure stable formation of color filter and lens parts, then the stability of color filter and lens part formation is improved, but the amount of light entering the light receiving element decreases

Engineering Contradiction:

Improvestability of color filter and lens part formationVSAvoidamount of light entering light receiving element

Core Design Contradiction:

Stability of the object's compositionVSIllumination intensity

Solution Approach 1:

The patent applies local quality by differentiating the treatment of the insulating layer between pixel regions and surrounding regions. The first insulating layer is selectively removed only in pixel regions to reduce thickness and improve light transmission, while maintaining sufficient thickness in surrounding regions for stable color filter and lens part formation. This localized differentiation resolves the contradiction between light transmission and structural stability.

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

If the insulating layer is made thick to shield light in surrounding region, then light shielding effect is improved, but cross-talk between adjacent unit pixels increases due to longer refraction path

Engineering Contradiction:

Improvelight shielding effect in surrounding regionVSAvoidcross-talk between adjacent unit pixels

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The patent implements local quality by selectively removing the first insulating layer only in pixel regions where light reception is needed, while preserving the insulating layer in surrounding regions for light shielding. This spatial differentiation allows the system to simultaneously achieve effective light shielding in surrounding regions and minimal cross-talk in pixel regions by optimizing the refraction path length locally.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent segments the insulating layer structure into multiple functional zones: the first insulating layer is selectively removed in pixel regions while maintained in surrounding regions, creating distinct optical paths. This segmentation allows independent optimization of light shielding and cross-talk prevention in different spatial zones.

Inventive Principle:

Principle #1Segmentation

3Illumination intensity

If the insulating layer is made thin to increase light transmission, then light reception sensitivity is improved, but the formation of color filter and lens parts becomes unstable

Engineering Contradiction:

Improvelight reception sensitivityVSAvoidformation stability of color filter and lens parts

Core Design Contradiction:

Illumination intensityVSStability of the object's composition

Solution Approach 1:

The patent applies local quality by creating different insulating layer thicknesses in different regions: thin insulating layers in pixel regions for high light transmission and sensitivity, and thick insulating layers in surrounding regions for stable color filter and lens part formation. This regional differentiation resolves the contradiction between light reception sensitivity and formation stability.

Inventive Principle:

Principle #3Local quality

4Object-affected harmful factors

If shielding metal layers are formed at different heights to maximize shielding, then light shielding in surrounding region is improved, but height difference creates step discontinuity affecting planarization

Engineering Contradiction:

Improvelight shielding in surrounding regionVSAvoidplanarization quality and surface flatness

Core Design Contradiction:

Object-affected harmful factorsVSManufacturing precision

Solution Approach 1:

The patent merges the first and second shielding metal layers by forming them at substantially the same height, eliminating step discontinuities. This consolidation maintains effective light shielding while ensuring surface flatness and planarization quality, resolving the contradiction between shielding effectiveness and manufacturing precision.

Inventive Principle:

Principle #5Merging (Combining)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach stabilizes the formation of color filter and lens parts, reduces cross-talk, and enhances light absorption by minimizing the interlayer dielectric thickness, thereby improving sensitivity and operational efficiency.

Implementation Method 1

a first shielding metal layer 220 stacked on the first insulating layer 210 for partly shielding incident light entering through the color filter part 30

Methodology Applied

Scientific EffectLight shielding: Absorption (EM radiation)